The invention relates to a machine for milling cereals, in particular rice, which belongs to the known type in which the milling material runs through an annular space which is bounded on the outside by an outer casing and on the inside by a milling rotor. The outer casing contains holes or slots through which the milled flour can emerge. The milling material is fed to the annular space at one end and led away from it at the other end. In the case of a known machine of this type (EP-B-521 452), the outer casing and the rotor are designed cylindrically and arranged vertically. The material is fed in a positively driven manner to the annular space at the bottom end by a screw conveyor. At the top end, the treated material emerges freely from the annular space. Filling of the annular space is ensured by the gravitational force, which is directed counter to the conveying direction. This arrangement has the disadvantage that the milling conditions cannot be adjusted optimally. It is not possible for the increase in the radial width of the annular space, said increase being caused by the gradual wear of the rotor, to be compensated for. Adaptation of the process parameters to different properties of the milling material is not possible.
This also applies in the case of known machines (prior public use) in which the cylindrical, vertically arranged annular space has material running through it from top to bottom. The material is fed merely by gravitational force, without any positively driven conveying operation. Its unobstructed emergence at the bottom end is prevented by a counterpressure disc, which closes off the bottom end of the annular space and can yield to the outlet pressure of the material, counter to a weight-loaded lever system. Experience shows that, despite the presence of the counterpressure disc, the annular space is not filled completely. As in the case of the abovementioned machine, the capacity is comparatively low, the broken fraction is high and a high temperature is also established.
Machines of which the annular space is designed conically are also known (prior public use). The material is fed, by gravitational force, to the top, large-diameter end. The bottom, small-diameter end is open. Complete filling of the working space, this filling being a prerequisite for high capacity, cannot be achieved. This disadvantage is not offset either by the advantage of the adjustability of the width of the annular space since, in the attempt to increase the capacity by reducing the width of the annular space, an excessively high working temperature is established. Reversing the cone arrangement does not provide improved properties either. Consequently, at the present time, high-quality manufacturers only provide machines with a cylindrical working space.